This invention relates to electrostatographic reproduction machines, and more particularly to a process cartridge for use in an electrostatographic reproduction machine. Specifically this invention relates to such a cartridge including a printing cartridge with two stage charging and metering of a development member.
Generally, the process of electrostatographic reproduction, as practiced in electrostatographic reproduction machines, includes charging a photoconductive member to a substantially uniform potential so as to sensitize the surface thereof. A charged portion of the photoconductive surface is exposed at an exposure station to a light image of an original document to be reproduced. Typically, an original document to be reproduced is placed in registration, either manually or by means of an automatic document handler, on a platen for such exposure.
Exposing an image of an original document as such at the exposure station, records an electrostatic latent image of the original image onto the photoconductive member. The recorded latent image is subsequently developed using a development apparatus by bringing a charged dry or liquid developer material into contact with the latent image. Two component and single component developer materials are commonly used. A typical two-component dry developer material has magnetic carrier granules with fusible toner particles adhering triobelectrically thereto. A single component dry developer material typically comprising toner particles only can also be used. The toner image formed by such development is subsequently transferred at a transfer station onto a copy sheet fed to such transfer station, and on which the toner particles image is then heated and permanently fused so as to form a "hardcopy" of the original image.
It is well known to provide a number of the elements and components, of an electrostatographic reproduction machine, in the form of a customer or user replaceable unit CRU. Typically such units are each formed as a cartridge that can be inserted or removed from the machine frame by a customer or user. Reproduction machines such as copiers and printers ordinarily include consumable materials such as toner, volume limiting components such as a waste toner container, and life cycle limiting components such as a photoreceptor and a cleaning device. Because these elements of the copying machine or printer must be replaced frequently, they are more likely to be incorporated into a replaceable cartridge as above.
There are therefore various types and sizes of cartridges, varying from single machine element cartridges such as a toner cartridge, to all-in-one electrostatographic toner image forming and transfer process cartridges. The design, particularly of an all-in-one cartridge can be very costly and complicated by a need to optimize the life cycles of different elements, as well as to integrate all the included elements, while not undermining the image quality. This is particularly true for all-in-one process cartridges to be used in a family of compact electrostatographic reproduction machines having different volume capacities and elements having different life cycles.
There is therefore a need for a quality image producing, economical and capacity-extendible all-in-one process cartridge that is easily adapted for use in various machines in a family of compact electrostatographic reproduction machines having different volume capacities and elements with different life cycles.
In single component development as described above, the particle of toner is charged prior to development of the toner onto the photoreceptive drum by rubbing the particle between a charge-metering blade and the magnetic roll. The charged particles on the periphery of the magnetic roll are then transferred onto the photoconductive drum at the charged portions of the surface of the photoconductive drum or the latent image to form the developed image on the photoconductive drum. The developed image is then transferred onto the substrate or paper. In the process of transferring the toner from the surface of the magnetic roll onto the paper, some of the toner remains on the surface of the magnetic roll. The toner, which remains on the surface of the magnetic roll, has a residual charge which may accumulate on the magnetic roll. When the surface of the magnetic roll is exposed to toner from the sump to be reloaded for further image development, the toner which remains on the surface combines with fresh toner from the sump. These accumulated or residual charges are not uniformly distributed on the periphery of the magnetic roll and in fact correspond to the developed image of the photoconductive drum. These accumulated or residual charges on the periphery of the magnetic roll cause less toner to be attracted to the periphery of the magnetic roll at areas which correspond to a concentrated or solid developed image of the photoconductive drum. These accumulated or residual charges may result in ghosting or underdevelopment of an area upon the substrate or paper.
Such ghosting phenomenon is more acute in solid area development where large areas of the substrate are required to have a dark or solid image. In such situations these accumulated or residual charges reduce the amount of fresh toner attracted onto the magnetic roll. This lack of sufficient toner on the magnetic roll result in insufficient toner being transferred to the photoconductive drum for transferring onto the substrate to obtain a proper image on the substrate. This phenomenon may be attributable to the fact that the magnetic roll may not pick up enough toner on areas of the magnetic roll which were previously used for solid area development. Therefore, these areas have a lighter than desired image. This phenomenon is commonly known as ghosting.
The following disclosures may be relevant to various aspects of the present invention: